HDD is a process were a drilling machine tunnels undrneath obtrusions such as a roadway, utilities,buildings and then pulls pipe back through the underground tunnel leaving the surface untouched. This process involves three main stages: Piloting (drilling of a pilot hole). Reaming (pilot hole enlargements in stages),and pullback (installation of the carrier pipe). The tunnels can be drilled in average depths ranging from 3 to 80 feet below the surface and up to 1800 feet in length.